5 pencils cost $7.80. Which equation would help determine the cost of 6 pencils?
There are several equations that could help determine the cost, each with a slightly different approach. We can write the fact that 5 pencils cost $7.80 as a proportion: $\dfrac{5}{\$7.80}$ Let $x$ represent the unknown cost of 6 pencils. Since 6 pencils cost $x$ , we have the following proportion: $\dfrac{6}{x}$ The cost changes along with the number of pencils purchased, and so the two proportions are equivalent. $\dfrac{5}{\$7.80} = \dfrac{6}{x}$